1. Field of the Invention
The present invention relates to sonar and radar type devices, and more particularly to a module for attachment to the radiating element of such devices for converging the beam to a narrower and less divergent beam.
2. Description of the Prior Art
Forward-looking sonar and radar devices are widely used for detecting objects that are not visible to the user. For example, sonar devices are used in commercial, military, and pleasure craft to detect underwater objects. In particular, a number of endangered mammals must be located by power craft at sufficient distance to avoid such mammals. Radar devices used for traffic control in current use have difficulty in discriminating among several vehicles, reducing the effectiveness of the tool.
The beamwidths of radiation from current sonars are too wide to pinpoint a mammal in sufficient time to avoid injury or death to the mammal. Thus, means are needed to reduce the beam angle of such sonars. For example, a typical 200 kHz unit utilizing a transducer having a diameter of about 2.325", produces an 8 degree beam. Applying prior art to reduce the beam angle to 1 degree would require a transducer having a diameter of about 17 inches. Such a large transducer is expensive, and it is difficult to obtain hydrodynamic stability in water with such a large device.
Doppler radar devices typically have broad beams of 12 to 40 degrees. Rust, in U.S. Pat. No. 2,785,397, teaches an external annular lens for reducing the beam angle. However, such a lens is too bulky for a hand held instrument commonly used for traffic control. Beam blocking and slicing techniques are taught by Pickering in U.S. Pat. No. 3,528,072. The size, weight and power loss of this approach makes it impractical. Other related U.S. patents include: U.S. Pat. No. 2,751,586 to Riblet; U.S. Pat. No. 2,801,412 to Mayburg; U.S. Pat. No. 2,840,811 to McMillan; and U.S. Pat. No. 5,113,197 to Luh. Schaufelberger, U.S. Pat. No. 3,833,909 teaches a rapidly scanning, wide angle, directional antenna system having a scanning horn, an inversion element, and coupled to a Luneberg lens type collimating device. Wolff, U.S. Pat. No. 2,206,683 includes a sectionalized horn fed by an adjustable attenuator.
Thus, an apparatus and method for reducing the beam angle of existing sonar and Doppler radar devices, using an add-on beam convergence device that does not significantly increase the physical size or cost of the device, is not taught by the known prior art.